Rats wrestling...

Question
I have two pet rats, both are about three months old and are girls. I know that they will wrestle and play fight, I have done my research on that front. But what is appearing strange is that one of them, Wanda, keeps trying to mount the other, Blu, and then bites her back. Blu then squeaks as if in pain. For the most part, they get along, they cuddle together and groom each other. But Wanda trying to hump Blu and keep her pinned down with her teeth in the process seems troublesome. Keep in mind, I have never owned rats before but always have wanted to. I just want to know if this is normal or something I should worry about. Any help would be great!

Answer
Completely normal :)  Most females can sense and smell when a cagemate is in heat and will play the mounting game.  Sometimes, cagemates take turns doing this to each other, and sometimes it is only one cagemate that does it to the other.  If the latter, then it's typically the more dominant female mounting the submissive one.

Females begin to go into heat at about 5 weeks of age.  They go into heat every 3 to 4 days, so you may notice this happening around this cycle.  This behavior can go on throughout the lives of your girls, but generally subsides once they get older.  

Please let me know if there is anything else I can help you with.